Should I say:
My hair was uneven for years.
My hair had been uneven for years.
For sure I'm talking about a time in the past.
With simple past, you are talking about the past from a perspective in the present:
My hair was uneven for years, but now I have cut it all off.
With past perfect, you are talking about a remote past, as seen from a more recent past:
Two years ago, when my hair had been uneven for years, I cut it all off.
Jack often has solid and correct answers. So I apologize that I will try to add. I am more simple than Jack, so I state things more simply, but I hope this is helpful.
The past perfect is for story telling. When you are telling a story of a past even, the past perfect it what you use to tell a story of the past INSIDE a story of the past. A dream within a dream. “Four years ago I thought about my past, I had been working for 2 years...”.
Past simple is more flexible but les precise. “I was working for two years.” Doesn’t say when. I could be from today. I could say “this happened back when I was working in japan for two years”. This could mean the event happened at any point in my two year stint working in japan.
My hair was uneven for years.- simple past tense
My hair had been uneven for years.- past perfect tense
It is better to use the simple past tense. 'My hair was uneven for years.'
Two actions happened in the past. We use the past perfect tense for the former action and the simple past tense for the later action.
Example of past perfect- My hair had been uneven for years. A few days ago my friend cut my hair off.
We can also use the simple past tense for both of the actions.
My hair was uneven for years. A few days ago my friend cut my hair off.